Bravo to Andris Nelsons, the febrile, 30-year-old Latvian who made his sensational Albert Hall debut last week. Bravo, too, to the City of Birmingham Symphony Orchestra, which he joined as charismatic music director last year. Just as you thought the Proms, 10 days in, were about to be strangled by their own thematic bindweed - anniversaries of every kind, a platoon of "complete cycles", plus a few frilly add-ons such as the theory of evolution - in roared a concert which cut through the thicket and reassured you that these programmes do have their stand-alone, free-spirited identities after all.

Nelsons's CBSO Prom 16 fitted perfectly and obediently into the season's schematic grid, with The Firebird, part of this year's Stravinsky ballet series, and Tchaikovsky's Second Piano Concerto, played by Stephen Hough, who will perform in all the composer's works for piano and orchestra across four Proms. Yet the moment Nelsons hunched his shoulders, lifted his baton in "on your marks" readiness, then leapt into whirligig action, you knew this would be a special event, one to stand out from the 76 concert-strong crowd.

So it proved. Opening with John Casken's atmospheric Orion Over Farne (1984), the CBSO captured the mystery and vastness of the Northumberland seascape that inspired the work, alive with glistening, tuned percussion, harp and piano and salty, plangent woodwind. Then Hough and Nelsons launched into the Tchaikovsky, an unbalanced but enthralling score with its ambitious, extended first movement, poetic but uneven middle and feverishly jaunty finale.

The piano part, and especially the first big cadenza, is so fast, complex and ferociously difficult that you feared Hough - or the instrument he was in brilliant combat with - would combust. But he and the orchestra somehow managed to plunge down the helter-skelter together with perfect grace and companionship, never appearing to falter. Afterwards, Hough played a slinky solo miniature by Mompou, as if offering us all a pianissimo tranquilliser.

In The Firebird, the CBSO again excelled, every detail of Stravinsky's tense, sensual score keenly defined, the players responding to each of Nelsons's acrobatic work-out gestures, so precise you would have known how the music sounded even if the orchestra had stopped playing. No wonder he's thin. At the end, the musicians at first refused to take their bow, clapping their young maestro with evident affection and admiration.

Earlier in the week, the BBC orchestras linked arms and twirled in the interweaving reel of Proms themes. The risk, without extreme vigilance, is that instead of offering infinite variety, all concerts begin to feel the same. Take last weekend's offerings (heard on Radio 3). The linking thread was England 1934, a musical crossroads of deaths and births. Elgar featured five times in four concerts. On Saturday (Prom 12) the BBC Philharmonic and Sir Charles Mackerras gave a blistering reading of Holst's The Planets, alongside Elgar and Delius. Next night (Prom 14), the National Orchestra and Chorus of Wales responded in kind with Holst's First Choral Symphony, a long-winded but agreeable Keats setting, plus more Elgar and Delius. You see the problem.

On Monday (Prom 15), the BBC Symphony Orchestra's quietly starry chief conductor Jiri Belohlavek joined the dance with Stravinsky's Petrushka and music by Martinu. His Concerto for Two Pianos (1943) fitted the music-for-multiple-pianos strand and it's the half-century anniversary of the composer's death to boot. (Apologies, I am beginning to bore myself here.) The soloists, Jaroslava Pechocova and Vaclav Macha, made light of the rapid, spinning cascades of the opening toccata and kept textures clear and buoyant. This striking piece whets the appetite for the BBCSO's Martinu Symphony Cycle at the Barbican next season, a sentence I never expected to write. Despite a few rough edges, the playing in Petrushka was vivid and assured right up to the abrupt ending, unconvincingly revised by Stravinsky in 1950. Belohlavek has a feel for the restless, mechanical momentum of this puppet-ballet music.

Petrushka springs from a commedia dell'arte world of charlatans and mountebanks, inhabited a century earlier in Donizetti's L'elisir d'amore, the tale of a miracle elixir and the poor, lovesick Nemorino. Peter Auty sang this touching role in Glyndebourne's 2007 production by Annabel Arden, first seen on tour and now making a main festival debut. If the updated staging feels a touch stolid, musically there are treats, with good ensemble singing and idiomatic conducting from Maurizio Benini. Luciano di Pasquale's oleaginous Dulcamara and Alfredo Daza's wolfish Belcore bring smiles. But their generous teamwork in guiding the Adina of Ainhoa Garmendia - a very late replacement for Ekaterina Siurina - proved the real tear-jerker.

The Spanish soprano seemed totally at home with the action, thanks to occasional, gentle strong-arming by her fellow cast members. No wonder she wept as she took her enthusiastic curtain call. We all, in the words of Nemorino's famous aria, shed "una furtive lagrima".